1. Field of the Invention
The invention relates to polyaromatic ethers, aromatic ether oligomers, phthalonitrile monomers containing aromatic ether oligomer spacers, thermosets made from such phthalonitrile monomers, and processes for making the same.
2. Description of the Prior Art
Phthalonitrile monomers and phthalonitrile polymers of various types are described generally in U.S. Pat. Nos. 3,730,946, 3,763,210, 3,787,475, 3,869,499, 3,972,902, 4,209,458, 4,223,123, 4,226,801, 4,234,712, 4,238,601, 4,259,471, 4,304,896, 4,307,035, 4,315,093, 4,351,776, 4,408,035, 4,409,382, 4,410,676, 5,003,039, 5,003,078, 5,004,801, 5,132,396, 5,159,054, 5,202,414, 5,208,318, 5,237,045, 5,242,755, 5,247,060, 5,292,854, 5,304,625, 5,350,828, 5,352,760, 5,389,441, 5,464,926, 5,925,475, 5,965,268, 6,001,926, and 6,297,298, all incorporated herein by reference.
The above references generally teach methods for making and polymerizing phthalonitrile monomers. Such monomers typically have two phthalonitrile groups, one at each end of a connecting spacer chain. The monomers can be cured, whereby the cross-linking occurs between cyano groups. These cross-linked networks typically have high thermal and oxidative stability.
Phthalonitrile monomers with aromatic ether oligomeric or polymeric spacers are expected to be useful because they are predicted to have low melting points. Phthalonitrile monomers with a large window between the melting point and the cure temperature are desirable to control the rate of curing and the viscosity during curing.
U.S. Pat. No. 4,259,471 to Keller et al. discloses a phthalonitrile monomer having a polyphenoxy spacer with from 1 to 10 phenyl groups in the spacer chain. The monomer is made by reacting 4-nitrophthalonitrile with an aromatic diol. The aromatic diol is a phenoxy chain with terminal hydroxy groups. The patent states that the aromatic diol can be made by an Ullmann synthesis. However, the patent does not teach how to make the aromatic diol with more than two phenylene groups. It is known in the prior art that an Ullmann synthesis can be used to create a single aromatic ether linkage by reacting a haloaromatic with a hydroxyaromatic in the presence of a stoichiometric amount of a copper complex. There are no known prior reports of the use of an Ullmann synthesis to make an oligomeric or polymeric aromatic ether containing three or more aromatic groups.
U.S. Pat. No. 6,297,298 to Keller et al. recites a phthalonitrile monomer having a polyphenoxy spacer as an embodiment of a general structure. The patent does not disclose any examples of or a process for making this phthalonitrile monomer.
The compound m-bis[m-(m-phenoxyphenoxy)phenoxy]benzene is a commercially available aromatic ether oligomer. There are no other known prior reports of other aromatic ether oligomers.
Marcoux et al., J. Am. Chem. Soc. 1997, 119, 10539, discloses a method for synthesizing a diaryl ether from a haloaromatic and a phenol using a catalytic amount of a copper complex and cesium carbonate. This method does not require the harsh conditions of an Ullmann synthesis such as high temperatures. The method also avoids the use of a stoichiometric amount of copper. The publication does not disclose any use of the method to make an aromatic ether oligomer.
There is need for process to make an aromatic ether oligomer and a polyaromatic ether. The resulting aromatic ether oligomer can then be reacted with a nitrophthalonitrile to make a phthalonitrile monomer. The phthalonitrile monomer can then be cured to form a thermoset.